RNO 54: A Previously Unappreciated FU Ori Star Hillenbrand, Lynne A.; Carvalho, Adolfo; van Roestel, Jan ...
Astrophysical journal. Letters,
12/2023, Letnik:
958, Številka:
2
Journal Article
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Abstract
We present evidence in support of the hypothesis that the young stellar object RNO 54 is a mature-stage FU Ori type source. The star was first cataloged as a “red nebulous object” in the ...1980s but appears to have undergone its outburst prior to the 1890s. Present-day optical and near-infrared spectra are consistent with those of other FU Ori-type stars, both in the details of spectral line presence and shape, and in the overall change in spectral type from an FGK-type in the optical, to the M-type presented in the near-infrared. In addition, the spectral energy distribution of RNO 54 is well-fit by a pure-accretion disk model with parameters:
M
̇
=
10
−
3.45
±
0.06
M
⊙
yr
−1
,
M
*
= 0.23 ± 0.06
M
⊙
, and
R
inner
= 3.68 ± 0.76
R
⊙
, though we believe
R
inner
is likely close to its upper range of 4.5
R
⊙
in order to produce a
T
max
=
7000
K that is consistent with the optical to near-infrared spectra. The resulting
L
acc
is ∼265
L
⊙
. To find these values, we adopted a source distance
d
= 1400 pc and extinction
A
V
= 3.9 mag, along with disk inclination
i
= 50 deg based on the consideration of confidence intervals from our initial disk model, and in agreement with observational constraints. The new appreciation of a well-known source as an FU Ori-type object suggests that other such examples may be lurking in extant samples.
Abstract
The nature of the peculiar “Ca-rich” SN 2019ehk in the nearby galaxy M100 remains unclear. Its origin has been debated as either a stripped core-collapse supernova or a thermonuclear helium ...detonation event. Here, we present very late-time photometry of the transient obtained with the Keck I telescope at ≈280 days from peak light. Using the photometry to perform accurate flux calibration of a contemporaneous nebular phase spectrum, we measure an O I luminosity of (0.19–1.08) × 10
38
erg s
−1
and Ca II luminosity of (2.7–15.6) × 10
38
erg s
−1
over the range of the uncertain extinction along the line of sight and distance to the host galaxy. We use these measurements to derive lower limits on the synthesized oxygen mass of ≈0.004–0.069
M
⊙
. The oxygen mass is a sensitive tracer of the progenitor mass for core-collapse supernovae, and our estimate is consistent with explosions of very low-mass CO cores of 1.45–1.5
M
⊙
, corresponding to He core masses of ≈1.8–2.0
M
⊙
. We present high-quality peak light optical spectra of the transient and highlight features of hydrogen in both the early (“flash”) and photospheric phase spectra that suggest the presence of ≳0.02
M
⊙
of hydrogen in the progenitor at the time of explosion. The presence of H, together with the large Ca II/O I ratio (≈10–15) in the nebular phase, is consistent with SN 2019ehk being a Type IIb core-collapse supernova from a stripped low-mass (≈9–9.5
M
⊙
) progenitor, similar to the Ca-rich SN IIb iPTF 15eqv. These results provide evidence for a likely class of “Ca-rich” core-collapse supernovae from stripped low-mass progenitors in star-forming environments, distinct from the thermonuclear Ca-rich gap transients in old environments.
We present observations of ZTF18abfcmjw (SN2019dge), a helium-rich supernova with a fast-evolving light curve indicating an extremely low ejecta mass ( 0.33 M ) and low kinetic energy ( 1.3 × 1050 ...erg). Early-time (<4 days after explosion) photometry reveals evidence of shock cooling from an extended helium-rich envelope of ∼0.1 M located ∼1.2 × 1013 cm from the progenitor. Early-time He II line emission and subsequent spectra show signatures of interaction with helium-rich circumstellar material, which extends from 5 × 1013 cm to 2 × 1016 cm. We interpret SN2019dge as a helium-rich supernova from an ultra-stripped progenitor, which originates from a close binary system consisting of a mass-losing helium star and a low-mass main-sequence star or a compact object (i.e., a white dwarf, a neutron star, or a black hole). We infer that the local volumetric birth rate of 19dge-like ultra-stripped SNe is in the range of 1400-8200 Gpc − 3 yr − 1 (i.e., 2%-12% of core-collapse supernova rate). This can be compared to the observed coalescence rate of compact neutron star binaries that are not formed by dynamical capture.
We present results from a search for a radio transient associated with the LIGO/Virgo source S190814bv, a likely neutron star-black hole (NSBH) merger, with the Australian Square Kilometre Array ...Pathfinder. We imaged a 30 deg2 field at ΔT = 2, 9, and 33 days post-merger at a frequency of 944 MHz, comparing them to reference images from the Rapid ASKAP Continuum Survey observed 110 days prior to the event. Each epoch of our observations covers 89% of the LIGO/Virgo localization region. We conducted an untargeted search for radio transients in this field, resulting in 21 candidates. For one of these, AT2019osy, we performed multiwavelength follow-up and ultimately ruled out the association with S190814bv. All other candidates are likely unrelated variables, but we cannot conclusively rule them out. We discuss our results in the context of model predictions for radio emission from NSBH mergers and place constrains on the circum-merger density and inclination angle of the merger. This survey is simultaneously the first large-scale radio follow-up of an NSBH merger, and the most sensitive widefield radio transients search to-date.
Abstract
We present Spitzer/InfraRed Array Camera observations of dust formation from six extragalactic carbon-rich Wolf-Rayet (WC) binary candidates in low-metallicity (
Z
≲ 0.65
Z
⊙
) environments ...using multiepoch mid-infrared (IR) imaging data from the SPitzer InfraRed Intensive Transients Survey (SPIRITS). Optical follow-up spectroscopy of SPIRITS 16ln, 19q, 16df, 18hb, and 14apu reveals emission features from C
iv
λ
5801−12 and/or the C
iii–iv
λ
4650/He
ii
λ
4686 blend that are consistent with early-type WC stars. We identify SPIRITS 16ln as the variable mid-IR counterpart of the recently discovered colliding-wind WC4 + O binary candidate, N604-WRXc, located in the subsolar metallicity NGC 604 H
ii
region in M33. We interpret the mid-IR variability from SPIRITS 16ln as a dust-formation episode in an eccentric colliding-wind WC binary. SPIRITS 19q, 16df, 14apu, and 18hb exhibit absolute 3.6 magnitudes exceeding that of one of the most IR-luminous dust-forming WC systems known, WR 104 (
M
3.6
≲ −12.3). An analysis of dust formation in the mid-IR outburst from SPIRITS 19q reveals a high dust production rate of
M
⊙
yr
−1
, which may therefore exceed that of the most efficient dust-forming WC systems known. We demonstrate that efficient dust formation is feasible from early-type WC binaries in the theoretical framework of colliding-wind binary dust formation if the systems host an O-type companion with high mass-loss rates (
M
⊙
yr
−1
). This efficient dust formation from early-type WC binaries highlights their potential role as significant sources of dust in low-metallicity environments.
Abstract
We present a systematic study of the most luminous (
M
IR
Vega magnitudes brighter than −14) infrared (IR) transients discovered by the
SPitzer
InfraRed Intensive Transients Survey (SPIRITS) ...between 2014 and 2018 in nearby galaxies (
D
< 35 Mpc). The sample consists of nine events that span peak IR luminosities of
M
4.5,peak
between −14 and −18.2, show IR colors between 0.2 < (3.6–4.5) < 3.0, and fade on timescales between 55 days <
t
fade
< 480 days. The two reddest events (
A
V
> 12) show multiple, luminous IR outbursts over several years and have directly detected, massive progenitors in archival imaging. With analyses of extensive, multiwavelength follow-up, we suggest the following possible classifications: five obscured core-collapse supernovae (CCSNe), two erupting massive stars, one luminous red nova, and one intermediate-luminosity red transient. We define a control sample of all optically discovered transients recovered in SPIRITS galaxies and satisfying the same selection criteria. The control sample consists of eight CCSNe and one Type Iax SN. We find that 7 of the 13 CCSNe in the SPIRITS sample have lower bounds on their extinction of 2 <
A
V
< 8. We estimate a nominal fraction of CCSNe in nearby galaxies that are missed by optical surveys as high as
(90% confidence). This study suggests that a significant fraction of CCSNe may be heavily obscured by dust and therefore undercounted in the census of nearby CCSNe from optical searches.
Abstract
AT 2020mot is a typical UV/optical tidal disruption event (TDE) with no radio or X-ray signatures in a quiescent host. We find an
i
-band excess and rebrightening along the decline of the ...light curve which could be due to two consecutive dust echoes from the TDE. We model our observations following van Velzen et al. and find that the near-infrared light curve can be explained by concentric rings of thin dust within ∼0.1 pc of a ∼6 × 10
6
M
⊙
supermassive black hole (SMBH), among the smallest scales at which dust has been inferred near SMBHs. We find dust covering factors of order
f
c
≤ 2%, much lower than found for dusty tori of active galactic nuclei. These results highlight the potential of TDEs for uncovering the environments around black holes when including near-infrared observations in high-cadence transient studies.
We present infrared (IR) photometry and spectroscopy of the Type II-P SN 2017eaw and its progenitor in the nearby galaxy NGC 6946. Progenitor observations in the Ks band in four epochs from 1 yr to 1 ...day before the explosion reveal no significant variability in the progenitor star greater than 6% that lasts longer than 200 days. SN 2017eaw is a typical SN II-P with near-IR and mid-IR photometric evolution similar to those of SNe 2002hh and 2004et, other normal SNe II-P in the same galaxy. Spectroscopic monitoring during the plateau phase reveals a possible high-velocity He i 1.083 m absorption line, indicative of a shock interaction with the circumstellar medium. Spectra between 389 and 480 days postexplosion reveal a strong CO first overtone emission at 389 days, with a line profile matching that of SN 1987A from the same epoch, indicating ∼10−3 M of CO at 1800 K. From the 389 days epoch until the most recent observation at 566 days, the first overtone feature fades while the 4.5 m excess, likely from the CO fundamental band, remains. This behavior indicates that the CO has not been destroyed, but that the gas has cooled enough that the levels responsible for first overtone emissions are no longer populated. Finally, the evolution of Spitzer 3.6 m photometry shows evidence for dust formation in SN 2017eaw, with a dust mass of 10−6 or 10−4 M assuming carbonaceous or silicate grains, respectively.
Calcium-rich gap transients represent an intriguing new class of faint and fast-evolving supernovae that exhibit strong Ca ii emission in their nebular phase spectra. In this paper, we present the ...discovery and follow-up observations of a faint and fast-evolving transient, iPTF 16hgs, that exhibited a double-peaked light curve. Exhibiting a Type Ib spectrum in the photospheric phase and an early transition to a Ca ii dominated nebular phase, iPTF 16hgs shows properties consistent with the class of Ca-rich gap transients, with two important exceptions. First, while the second peak of the light curve is similar to other Ca-rich gap transients, the first blue and fast-fading peak (declining over 2 days) is unique to this source. Second, we find that iPTF 16hgs occurred in the outskirts (projected offset of 6 kpc 1.9 Reff) of a low-metallicity ( 0.4 Z ), star-forming, dwarf spiral galaxy. Deep limits from late-time radio observations suggest a low-density environment for the source. If iPTF 16hgs shares explosion physics with the class of Ca-rich gap transients, the first peak can be explained by the presence of 0.01 M of 56Ni in the outer layers the ejecta, reminiscent of some models of He-shell detonations on WDs. However, if iPTF 16hgs is physically unrelated to the class, the first peak is consistent with shock cooling emission (of an envelope with a mass of 0.08 M and radius of 13 R ) in a core-collapse explosion of a highly stripped massive star in a close binary system.
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